The present invention relates to a highly reliable and, at the same time, easily manufacturable interconnection in which copper or a copper alloy is utilized.
Copper and copper alloys containing tin or such in addition to copper have come into wider use for interconnections of the integrated circuits, in place of aluminium, to serve as high-performance and, at the same time, highly reliable interconnections for the LSIs (Large Scale Integrated Circuits), since they have lower resistances than those of aluminium and aluminium alloys as well as high resistances against migration (electromigration and stressmigration).
For the aluminium-based interconnections, with the object of improving reliability of interconnections, good efforts have been being made to form, satisfactorily, films of the large grain size and highly  less than 111 greater than  oriented films. The use of a film of the large grain size which shows, at the same time, high preference of the  less than 111 greater than  texture has, in essence, an effect equivalent to a reduction of the grain boundaries of the high migration velocity for atoms.
In general, the migration velocity for atoms which pass through a random grain boundary, separating adjacent crystal grains between which a large difference in orientation (misorientation) is present and any specific orientational relationship is absent, or a grain boundary in weak orientational relationship (a grain boundary having a large xcexa3-value, a xcexa3-value being defined as the reciprocal number of the density for coincident lattice sites in so-called coincident grain boundary) is markedly high in comparison with that for atoms which pass through a lattice or coincident grain boundary having a small xcexa3-value.
Accordingly, for the wide interconnections such as the interconnection used for the power supply line (generally said as the interconnections having a width greater than the average grain diameter or the interconnections with polygranular grain boundary structures) where the migration for passing through grain boundaries is dominant, the reduction of such grain boundaries of the high migration velocity for atoms is considered to be one of the standard strategies for enhancing the migration resistance.
When the line width becomes less than the average grain diameter, the grain boundary structure of the interconnection takes a near-bamboo grain boundary structure wherein polygranular grain boundary sections and bamboo grain boundary sections mix, while, in the interconnection with a still narrower width, it takes a bamboo grain boundary structure comprising hardly any polygranular grain boundary sections. In the interconnection with a near-bamboo grain boundary structure, the migration resistance is basically determined by the migration velocities to pass through grain boundaries in the polygranular grain boundary sections.
As against this, in the bamboo grain boundary interconnection, because there exists no continuous grain boundary running from end to end in the direction of the interconnection length, the long-range migration for atoms basically depends on the migration to pass through interfaces between interconnection metals and insulating films and/or interfaces between layers of a multi-level interconnection metal.
Further, with respect to the short-range migration from the inside of the interconnection to the interface, a large component thereof is considered to pass through bamboo grain boundaries so that, in this case, too, the increase of coincident grain boundaries having small xcexa3-values, in other words, the strengthening of the  less than 111 greater than  orientation is regarded as an effective means to achieve the enhancement of migration resistance, though not so effective as for the polygranular interconnection.
The migration resistance depends on not only the migration velocities as described above but also the degree of liability and the actual place of the void creation. Voids are liable to form at the intersections of the grain boundaries with the interconnection surfaces (including lateral and bottom faces). Since voids are particularly apt to form at the places where random grain boundaries or coincident grain boundaries having large xcexa3-values intersect with the surfaces, the strengthening of the  less than 111 greater than  orientation and its resultant reduction of such grain boundaries are also regarded as an effective means to achieve an improvement of the migration resistance.
Similarly, for the copper interconnections, an application of a film of the large grain size for the purpose of enhancing the migration resistance (Japanese Patent Application Laid-open No. 315327/1993) and a method of forming a film of the large grain size, which shows, at the same time, high preference of the  less than 111 greater than  orientation (Japanese Patent Application Laid-open No. 125954/1989) have been reported. Further, there have been reported that an use of a copper film having a percentage of the  less than 111 greater than  orientation of 90% or greater heightens the acid resistance of the Cu interconnection (Japanese Patent Application Laid-open No. 275617/1994), or enhances the migration resistance thereof (Japanese Patent Application Laid-open No. 27656/1986).
Nevertheless, the present inventors found out that, in the case of the copper interconnection, the formation of a film of the large grain size, which has, at the same time, orientation with strong preference for one direction, is not so easy as that in the case of the aluminium interconnection, and this gives rise to a problem that a specific manufacturing step must be additionally introduced or conditions of manufacturing steps must be limited to a narrower range.
An object of the present invention is to provide a highly reliable and, at the same time, easily manufacturable interconnection containing copper or a copper alloy, without utilizing a film having orientation with particularly strong preference for one direction, which is difficult to manufacture but has been sought after in the conventional techniques.
The present invention, which is to attain the above object, provides an interconnection comprising a copper or copper alloy layer, wherein at least 50% of crystal grains of copper or a copper alloy form twins.
The present invention can, thereby, provide a copper or copper alloy interconnection which is highly reliable and, at the same time, manufacturable at low production cost.